The invention relates to a mixer and more particularly to a mixer for constructional materials comprising a driven drum which is rotatably mounted on a yoke pivoting on a frame and is able to be driven by means of a frame-mounted drive device including an air-cooled electric motor which motor is arranged in a frame mounted encapsulating means, provided with a switch and plug unit and having an air intake opening and an air outlet opening, and which motor is adapted via a countershaft transmission to drive a drive shaft which is associated with the drum and whose axis of rotation coincides with the pivot axis of the yoke.
In the case of a known arrangement of this type the encapsulating means takes the form of a synthetic resin housing, which only accommodates the motor. The countershaft transmission is not included within it. Accordingly the synthetic resin housing for the motor is located within a second protective housing, which also covers the countershaft transmission. This second protective housing is however open in a downward direction in order to provide for access to the switch and electrical plug unit mounted on the synthetic resin housing constituting a shroud around the motor. In order to form the air intake opening and the air outlet opening there are in this case slots constituted by a cover, which defines a gap, and respectively by wall cutouts. In the case of the known arrangement there is the likelihood of water being splashed upwards into the outer guard housing. Thus on the one hand this splashed water may spread out along the parts of the transmission so that there is the danger of the insulating function performed by the parts of the transmission being overridden by such creeping water and furthermore it is possible for the water to leak into the electric motor itself. Furthermore on the other hand there is the substantial chance of water being splashed directly into the electric motor through the air intake and outlet openings. The consequence of this may well be a short circuiting of the motor and the formation of water film bridges and hence damage to the motor or an impairment of the protective insulation. There is also the danger that anyone poking a thin metal object into the enclosure such as a piece of wire may make contact with a live part, since parts of this type may be introduced into the synthetic resin housing and through the air intake and air outlet openings. The known arrangement has therefore not proved to be sufficiently safe.
A further disadvantage is to be seen in the fact that the switch and plug unit arranged on the synthetic resin housing covered by the outer protective housing is not very accessible and may only be seen on stooping. The known arrangement is thus awkward to use. Nevertheless the known arrangement involves a comparatively elaborate design, since in addition to the synthetic resin housing for the motor there is also the requirement for a second protective housing accommodating the countershaft transmission and the synthetic resin housing. This disadvantage is made even more serious since the switch and plug unit is molded on the synthetic resin housing. It is consequently necessary to provide an assortment of different synthetic resin housings for adaptation to the switch and plug units complying with the various national technical standards.